1. Field of the Invention
This invention relates to an image correction apparatus for the adjustment of an image which is received and displayed on a color television receiver, and particularly to a digital image correction apparatus which controls various correction waveforms in a digital manner, thereby implementing accurate and automatic image correction.
2. Description of the Prior Art
Generally, a video projector which performs enlarged projection on a screen by using three projection tubes, which emit three primary colors, involves such adversities as displacement of colors, out-of-focus, distortion of deflection and variation of brightness across the screen due to different incident angles termed "convergent angles" to the screen among the projection tubes. Although these various adverse phenomena are corrected based on the creation of analog correction waveforms in synchronism with the horizontal and vertical periods, this approximate correction scheme suffers in accuracy. Another problem is a long adjustment time is required for each item of correction because of the manual correcting operation through the visual observation of the screen. To cope with this problem, there are proposed a digital convergence apparatus in JP-B2-59-8114 as a method providing high convergence accuracy, and a digital convergence apparatus in JP-A-56-157188, as a method of automatic correction.
The conventional image correction apparatus will be explained with reference to the block diagram of FIG. 16. In a video projector formed of a projection display unit 7 and a screen 6, a pattern generator 25 projects pattern signals for items of correction on the screen so that the operator visually detects the amount of deviation and its change, and a convergence correction circuit 1, luminance correction circuit 2, focus correction circuit 3 and deflection correction circuit 4 are operated through the entry of correction data on a manual adjustment unit 5.
This apparatus, which bases the corrective operation of each item on the visual observation, performs accurate image correction. However, such a conventional image correction apparatus needs the entry of various correction data against the displacement of colors, out-of-focus, distortion of deflection and variation of luminance for each adjustment point on the screen, and therefore a long adjustment time is required and necessitates a large-scale circuit for the adjusting function of each mode.